The present invention relates to an endless, unwoven papermaker press felt that is employed in papermaking apparatus and that is utilized for carrying sheets or webs of paper in the fabrication thereof.
The use of papermaking press felts in the manufacture of paper has been well known in the papermaking field for many years. Because of the relatively large quantities of water that are used in the manufacture of paper sheets, the press felt as utilized for carrying the material from which the paper sheet is made must be constructed in such a manner as to enable water to be easily expressed from the felt as the material is fed through the nip rollers of the press machine. Further, it is desirable in the fabrication of paper sheet to avoid marking of the sheet as the material is fed through the nip rolls. Marking can occur if the press felt is formed of a woven material, for example, which necessarily includes so-called "knuckles" and that tend to project into the upper surface of the felt thereby marking the paper sheet as the sheet is fed through the nip rolls.
Some efforts have been made heretofore to avoid the use of woven materials in a papermaking felt, and one such unwoven papermaker's felt is illustrated and described in U.S. Pat. No. 3,097,413. As described in U.S. Pat. No. 3,097,413, the use of the unwoven endless press felt avoided the need for weaving equipment normally associated with the prior known woven felts. Various other types of press felts have been developed using unwoven layers of material, and one such press felt is illustrated in U.S. Pat. No. 4,555,440. In this patent, the press felt as disclosed avoids the use of woven materials but binds the adjacent layers by a binding thread which is passed perpendicularly through the layers and extends in the cross machine direction relative thereto. Other kinds of unwoven and similar types of papermaking press felts of which applicant is aware are illustrated in U.S. Pat. Nos. 2,943,379; 3,086,276; 3,331,140; 3,392,079; 3,401,467; 3,629,047; 3,657,068; 3,772,746; 4,224,372; 4,503,113 and 4,541,895.
Although the press felts as illustrated and described in the aforementioned U.S. patents have performed satisfactorily for limited purposes, they have not been totally satisfactory from a commercial point of view and are difficult to fabricate with present known equipment and, furthermore, are relatively expensive in the manufacture thereof. As will be described hereinafter, applicant's unique press felt avoids the problems of the prior known felts and provides a press felt of composite structure that is so constructed as to readily accept water, hold it in the void areas of the felt, and quickly release it from the backside of the felt so that improved results are obtained in the papermaking operation, while at the same time presenting an exceptionally smooth felt surface to the paper sheet. The present invention also avoids any unevenness in the surface thereof that may result from the use of weaving looms, and further eliminates the need for any special joining process.